1. Field of the Invention
This invention relates to memory modules for expanding memory capacity in computer systems and to memory module connectors.
2. Description of the Related Art
Both single in-line memory modules (SIMMs) and dual in-line memory modules (DIMMs) and corresponding memory module connector sockets for expanding memory with computer systems are well known. Generally speaking, in-line memory modules include a printed circuit board on which a plurality of memory chips such as DRAMs are surface mounted. A connective portion along one edge of the printed circuit board is adapted for insertion into a mating (i.e. accommodating) space of a connector. A plurality of contact pads (also called pins) on the connective portion mates with a plurality of corresponding contacts inside the accommodating space of the connector to provide for the transfer of electrical signals between the memory module and the rest of the computer system.
On a SIMM, the connective portion usually includes a plurality of contact pads on either the front side of the edge of the printed circuit board or on both the front and back sides of the printed circuit board. In configurations that include contact pads on both the front and back sides of a SIMM, opposing contact pads on the two sides are typically shorted together and therefore carrying the same electrical signal. In a DIMM, the contacts are positioned in the connective portion on both the front and back sides of the printed circuit board. At least some of the opposing contact pads on the two sides of the printed circuit board of a DIMM are configured to carry differing electrical signals, thereby increasing the signal density without necessitating smaller contact pads or a larger printed circuit board.
FIGS. 1A and 1B illustrate two embodiments of prior art DIMM memory modules 100 and 150, respectively. Memory modules 100 and 150, as shown, include 84 contact pads, such as contact pads 115A and 165A, on the front side, for 168 total contact pads. It is noted that the number of contact pads may vary such that memory modules with up to 200 contact pads are available on the market.
Memory modules 100 and 150 are configured to couple to appropriate memory module connectors, which are specifically designed to mate and secure the memory module. In general, a connector comprises a housing including an accommodating space, which is adapted to receive a portion of the printed circuit board of the memory module.
Turning to FIG. 1A in detail, memory module 100 includes a printed circuit board 110. A region 103, shown with dashed lines, for the placement of semiconductor integrated circuits, such as DRAM memory chips or other appropriate memory, occupies the majority of the space on a face of the printed circuit board 110. The contact pads 115 are disposed along one edge (i.e. the connective portion) of the printed circuit board 110 from a short distance from the left end to approximately the same distance from the right end. The center of the length of the printed circuit board 110 is marked with a centerline 101. A single notch 120 is positioned along the one edge at substantially the center of the edge of the printed circuit board 110. In other known embodiments, notch 120 may alternatively be positioned approximately one-half of the width of the notch to either side of the center location, as noted with dashed lines. Additional details regarding the notches 120 may be found with respect to FIG. 1C below. The printed circuit board 110 also includes indentions 105A and 105B positioned on the left end and right end, respectively. The indentations 105A and 105B are shaped to receive module extractors, which may be included as a part of the connector, to hold the memory module 100 in place when the module extractors are in a closed position.
Turning to FIG. 1B in detail, memory module 150 includes a printed circuit board 160. The contact pads 115 are disposed along one edge of the printed circuit board 160. The center of the length of the printed circuit board 160 is marked with a centerline 151. A center notch 120A is positioned along the one edge at substantially the center of the edge of the printed circuit board 160. Memory module 150 also includes a left notch 120B positioned to the left of center. Similar to the center notch 120A, the location of the left notch 120B is also known in other embodiments to be repositioned approximately one-half of the width of the notch 120B to either side of the illustrated location. The printed circuit board 160 also includes indentions 105C and 105D positioned on the left end and right end, respectively.
FIG. 1C is a close-up view of a notch 120. As shown, notch 120 is located on the edge of the printed circuit board 110 or 160 in a space along the row of contact pads 115. The height of the notch 120 is just slightly higher than the corresponding size of the contact pads 115.
It is noted that the notches 120 are configured to mate with keys in the accommodating space in the housing of the corresponding connector. A center key, which is configured to mate with a center notch 120 or 120A, of the connector may be referred to as the "voltage key", while the left key, which is configured to mate with left notch 120B, may be referred to as the "functionality key". The names refer to the different voltages and/or functionalities that the three locations for each key (and therefore notch) correspond, depending on the manufacturer or standard.
One problem associated with the memory modules 100 and 150 is the difficulty in correctly installing the memory module 100 or 150 in the corresponding connector. Even with installation guides as a part of the connector, the memory module 100 or 150 may be installed backwards or unevenly. While the use of a polarized two-notch memory module, such as memory module 150, may decrease the likelihood of installing the memory module backwards, the notches 120A and 120B may not aid in installing the memory module evenly. It may be possible to install the memory module 150 with a slight tilt leading to one or more misconnections or even shorts. A related problem is the stability of the memory module 100 or 150 once inserted in the corresponding connector. Additional stabilizing features may inhibit simple and accurate insertion, which may further lead to uneven insertion and improper connections. Thus, it can be seen that an improved memory module, connector, and system thereof with improved ease of insertion and stability are desired.